Knitting machines having sinkers which, relative to the needles, are quite short and located between the needles, are known. The movement of the needles and of the sinkers, respectively, is controlled by the needle cams and sinker cams. The sinkers are located to be longitudinally movable and, additionally, to be pivotable about an axis transverse to the longitudinal extent of the needles. During some portions of the needle movements, the sinkers move counter to the direction of the needles. To permit adjustment of the machines, it is also known to so construct the cam parts carrying the needle and sinker cams, respectively, that they can be adjusted with respect to each other. Such adjustment may permit change of the length of the stitches or loops being knitted, and thus changing the characteristics and/or the quality of the fabric which is being made.
Such knitting machines, such as are known in a specialized form from U.S. Pat. No. 4,608,841, Buck, to which German Patent No. DE-PS 33 30 530 corresponds, make it possible, because of the counter-directed movement of the needles and sinkers, to use relatively short needle movements and hence quite flat needle and sinker cam control tracks, which allows a substantial increase in the knitting speed as compared with knitting machines in which the needles, in the usual manner, execute a long stroke with respect to a fixed casting-off ridge. In order to avoid abrupt changes in motion of the needles and sinkers, the needle and sinker cam control tracks can also be embodied as substantially sinusoidal, as is described in U.S. Pat. No. 4,633,684, Kuhn, to which detail in German Patent No. DE-PS 35 10 054 corresponds.
In these knitting machines operating with contrary needle and sinker movement, it is generally true that a complete knit stitch or loop can be formed in a region of the needle cam control track extending over only one needle cut, and as a consequence the yarn can be handled very gently during loop formation. Because of the short needle and sinker movements, these machines also permit a relatively high density of feeds, which means that 120 or more feeds can be accommodated on the 30-inch-diameter needle cylinder of a circular knitting machine of this kind.
In practice, the need often arises of changing the loop length, or in other words the tightness of the goods, as needed. In such machines with numerous feeds, this conversion often entails a considerable expenditure of time, which is considered a disadvantage.
It's also known to prove, in a knitting machine, having oppositely directed needle and sinker movement. This machine provides for a central loop adjustment for all knitting feeds. The cam parts for the sinkers and the cam parts for the latch needles are located on separate cam carriers, which are adjustable both in the longitudinal direction of motion of the sinkers and needles and transversely thereto. Additionally, the cam parts for the sinkers and/or the latch needles have knock-over cam parts adjustable in a known manner with respect to the cam carriers, the cam part arrangement being such that the needle movement curve and the sinker movement curve, at the end of the portions of their movement counter to one another, can have loop forming points, or positions that match one another in the forward direction. The mutual adjustability of the needle and sinker cam carrier, both in the longitudinal direction of motion of the sinkers and needles and transversely thereto, requires two separate adjustment apparatuses and hence a considerable expense for construction (see German Patent Disclosure No. DE-OS 34 33 290). Less expense for the central loop adjustment is obtained in a multi-feed circular knitting machine known from British Patent No. 2,158,106, to which East German Patent No. DD-PS 224 889 corresponds. In this machine, for loop adjustment either a sinker cam ring is rotated in the circumferential direction relative to the stationary cylinder cam, or conversely the cylinder cam is rotated relative to the stationary sinker cam. The cylinder cam and the sinker cam are located on separate cam carriers, so that complicated adjusting gears and the like can be dispensed with.
The cam parts for the needles and sinkers are embodied such that the travel distance necessary for forming a loop is covered partly by the yarn-carrying needles and for the remainder by the sinkers; after attaining the loop forming position, the sinkers along with the needles are moved downward in the same direction to initiate the stitch or loop transfer. The arrangement is such that at each feed, the rising slope of the sinker cam track or cam control track, formed of identical portions, is selected to be steeper after reaching the loop forming position than the portion, aligned in the same direction, of the needle cam track or cam control track, while the rising slope of the singer cam track or cam control track, in the vicinity of the maximum needle projection during knitting or yarn seizing, is approximately equal to zero over approximately one-ninth to one-seventh the width of one feed. The sinker cam track or cam control track and/or the needle cam track or cam control track is displaceable, per feed and/or in its entirety, in the circumferential direction by a distance that is equivalent to approximately one-ninth to one-seventh the width of one feed.
Although the tightness of the goods can be changed rapidly as needed by simple means in this circular knitting machine, nevertheless disadvantages in terms of loop or stitch formation, resulting from the specialized shape of the needle and sinker cam curves or cam control tracks, must be accepted into the bargain.
Finally, U.S. Pat. No. 3,837,185 also discloses a circular knitting machine in which relatively long sinkers cooperate with the needles, the needles being movable axially parallel and aligned lengthwise on the needle cylinder, and the sinkers being movable obliquely to the needles and pointing radially outward from them and supported displaceably in a sinker ring. In this knitting machine, once the needles reach their lowermost reversal point, equivalent to the lowest draw-off position, they are initially moved upward together with the sinkers, in the course of which, because of their oblique position, they increasingly seize the yarn forming the new loop. Aside form the difficulty of overseeing the entire machine because of the oblique arrangement of the sinkers and the necessarily resulting invariable mutual dependency of the longitudinal and transverse motion of the sinkers on one another, this knitting machine has no possible means for changing the tightness of the goods.